When claiming the tax allowance, in some questions it is claimed from year Zero and other commence from year one, how can I determined which year we should start to claim the capital allowance on an asset for NPV
The main thing is what the question says – either that tax is payable immediately, or that tax is payable one year in arrears.
The second thing is the date on which the asset is purchased. If tax is payable immediately, then if the asset is purchased on the first day of an accounting period the first CA saving will be at time 1, but if the asset is purchased on the last day of an accounting period then the first CA saving will be at time 0. (However this second thing is only really relevant in the exam if it is a lease and buy question.)
Have you watched my lecture on lease and buy where I explain the tax timing?